Increasing numbers of adolescents approve of and use marijuana, and report that marijuana is relatively easy to obtain. Because marijuana use is associated with a host of negative consequences, many prevention campaigns have been implemented over the years, but most have been proven ineffective. We believe the failure of many campaigns is due to the common practice of assuming that the same message will successfully persuade a diverse audience of adolescents. This application seeks to prevent marijuana use by developing and testing a theory-based Tailored Interactive Media Intervention (TIMI) that avoids this common shortcoming. This intervention combines two theories that individually have been shown to have powerful effects on attitude change. In combination, they provide the means necessary to stem the accelerated tide of adolescent marijuana use that is evident in today's social statistics. The approach begins by either reinforcing anti-marijuana beliefs or weakening pro-marijuana beliefs. A second message, tailored to account for each participant's view of the normative nature of peer marijuana use, is then delivered. For pro-marijuana youth, this message attacks an attitude weakened by the first communication. Our approach is based on the resistance appraisals model (RAM), which specifies strategies to reduce resistance to persuasion, and the deviance regulation model (DRM), which guides the ways messages should be framed to account for differences in adolescents' perceptions of peer norms. Experiment 1 tests the utility of these theories separately in a marijuana prevention context. Experiment 2 tests the effects of combining the theories in developing a TIMI, and follows with a test of the effect of administering the TIMI repeatedly over the course of a school year. Outcomes include attitude toward marijuana, attitude certainty, intention to use marijuana, and actual usage. This approach overcomes resistance by reducing attitude certainty, and it creates maximally persuasive messages by accounting for and capitalizing on individually perceived peer norms, to which adolescents are exquisitely attuned. It outlines a feasible and cost- effective way of preventing adolescent marijuana use on a large scale by weakening and then directly targeting pro-drug attitudes in a manner that is widely applicable for all school-attending adolescents, a group in which marijuana use has risen significantly and dramatically over the past 4 years.